Update onboarding.md

aw-design-diagram/onboarding.md

 # Onboarding Diagram
-
+```mermaid
     flowchart LR
         subgraph AA["Authentication & Authorization"]
         g-reg["Registration"]
@@ -46,3 +46,4 @@
         p-afj["Mobile Aries Agent"]-- "Registration connection" -->AISBL
         p-afj-- "Subscription Connection" -->v-afj
         end
+```